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How Eye Dominance Strength Modulates the Influenceof a Distractor on Saccade Accuracy

Jérôme Tagu, Karine Doré-Mazars, Christelle Lemoine-Lardennois, DorineVergilino-Perez

To cite this version:Jérôme Tagu, Karine Doré-Mazars, Christelle Lemoine-Lardennois, Dorine Vergilino-Perez. How EyeDominance Strength Modulates the Influence of a Distractor on Saccade Accuracy. InvestigativeOphthalmology & Visual Science, Association for Research in Vision and Ophthalmology, 2016, 57(2), pp.534-543. �10.1167/iovs.15-18428�. �hal-01486582�

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How eye dominance strength modulates the influence of a distractor on 2

saccade accuracy 3

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Jérôme Tagu1, Karine Doré-Mazars1, Christelle Lemoine-Lardennois1 & Dorine 6

Vergilino-Perez1,2 7

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1Laboratoire Vision Action Cognition, EA n°7326, Institut de Psychologie, IUPDP, 9

INC, Université Paris Descartes, Sorbonne Paris Cité 10

2Institut Universitaire de France 11

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Correspondence should be addressed to: 14

Jérôme Tagu, [email protected] 15

Laboratoire Vision Action Cognition, EA n°7326, Institut de Psychologie, Université 16

Paris Descartes 17

71 av. Edouard Vaillant, 92774 Boulogne-Billancourt-Cedex, France 18

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Manuscript information: 24

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Title: 86 characters. 26

Abstract: In English: 217 words. In French: 248 words. 27

Revised text: 3765 words. 28

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Abstract 29

Purpose. Neuroimaging studies have shown that the dominant eye is preferentially 30

linked to the ipsilateral primary visual cortex. However, its role in perception is still 31

misunderstood. Here we examine the influence of eye dominance and eye 32

dominance strength on saccadic parameters, contrasting stimulations presented in 33

the two hemifields. 34

Methods. Participants with contrasted eye dominance (left or right) and eye 35

dominance strength (strong or weak) were asked to make a saccade toward a target 36

displayed at 5° or 7° left or right of a fixation cross. In some trials a distractor at 3° of 37

eccentricity was also displayed either in the same hemifield as the target (to induce a 38

global effect on saccade amplitude) or in the opposite hemifield (to induce a remote 39

distractor effect on saccade latency). 40

Results. Eye dominance did influence saccade amplitude as participants with strong 41

eye dominance showed more accurate saccades toward the target (weaker global 42

effect) in the hemifield contralateral to the dominant eye than in the ipsilateral one. 43

Such asymmetry was not found in participants with weak eye dominance or when a 44

remote distractor was used. 45

Conclusions. Here we show that eye dominance strength influences saccade target 46

selection. We discuss several arguments supporting the view that such advantage 47

may be linked to the relationship between the dominant eye and the ipsilateral 48

hemisphere. 49

Keywords: Eye dominance, Asymmetry, Saccadic eye movements, Distractor, Global 50

effect 51

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Résumé 52

Introduction : La neuroimagerie suggère qu’il existe une relation privilégiée entre l’œil 53

dominant et le cortex visuel primaire ipsilatéral. Cependant, le rôle de la dominance 54

oculaire dans notre perception et notre action reste mal connu. La présente étude 55

vise ainsi à étudier l’influence de la dominance oculaire et de sa force sur les 56

paramètres saccadiques en manipulant l’hémichamp visuel dans lequel apparaissent 57

les stimuli. 58

Méthode : 92 participants étaient répartis en quatre groupes selon leur dominance 59

oculaire (gauche ou droite) et sa force (forte ou faible). Leur tâche consistait à 60

effectuer une saccade vers une cible présentée à 5° ou 7° d’excentricité, à gauche 61

ou à droite d’une croix de fixation. Dans certains essais, un distracteur présenté à 3° 62

accompagnait la cible, dans le même hémichamp (afin d’induire un effet global) ou 63

dans l’hémichamp opposé (afin d’induire un remote distractor effect). 64

Résultats : Chez les participants ayant une forte dominance oculaire, les saccades 65

étaient plus précises (moins d’effet global) lorsqu’elles étaient dirigées vers une cible 66

présentée dans l’hémichamp controlatéral à l’œil dominant que dans l’hémichamp 67

ipsilatéral. Cet effet n’était en revanche pas présent chez les participants ayant une 68

faible dominance oculaire. Par ailleurs, aucune différence entre hémichamps n’a été 69

trouvée sur la latence des saccades lors de la présentation d’un distracteur éloigné. 70

Conclusion : Cette étude montre que la force de la dominance oculaire module la 71

précision de la sélection saccadique. Nous suggérons que cette modulation soit due 72

à la relation privilégiée entre œil dominant et hémisphère ipsilatéral. 73

Mots-clés : Dominance oculaire, Asymétrie, Saccades oculaires, Distracteur, Effet 74

global 75

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1. Introduction 76

The sighting dominant eye (DE) is the one chosen when performing a 77

monocular task. It is classically determined based on the “hole-in-the-card test”1, 78

which provides a binary measure: left or right DE, according to the eye chosen by the 79

participant for sighting through the hole in a piece of cardboard. However, it has 80

recently been suggested that eye dominance could be assessed more precisely with 81

binocular recordings2. Participants are categorized according to eye dominance 82

strength (i.e., strong or weak eye dominance) based on the analysis of the peak 83

velocity of saccades directed toward an isolated target. Indeed, participants exhibiting 84

higher peak velocities toward the hemifield ipsilateral to the DE whatever the eye 85

being measured are considered as having strong eye dominance, while participants 86

exhibiting higher peak velocities toward the left hemifield with the left eye and toward 87

the right hemifield with the right eye (i.e., standard naso-temporal asymmetry3) are 88

considered as having weak eye dominance2. 89

DE has also been studied with neuroimaging data, showing that it activates a 90

greater part of the primary visual cortex (V1) than the non-dominant eye4. Other 91

evidence5,6 suggests that the V1 ipsilateral to DE is larger5 and more activated6 than 92

the V1 contralateral to DE, suggesting a privileged relationship between DE and 93

ipsilateral V1. Due to the crossing of the optical pathways, the V1 ipsilateral to DE 94

initially processes information presented to the hemifield contralateral to the DE. 95

Recently, it has been examined whether such a relationship could lead to differences 96

in the visuomotor processing of information from the hemifield ipsilateral or 97

contralateral to DE7. Using the Poffenberger paradigm (manual response to a target 98

presented either in the left or in the right hemifield, using either the right or the left 99

hand8), participants exhibited faster reaction times when the target was presented in 100

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the hemifield contralateral to the DE than in the ipsilateral one7. The authors suggest 101

that this advantage of the hemifield contralateral to the DE over the ipsilateral one is 102

linked to the relationship between DE and ipsilateral V1. Indeed, this relationship 103

would lead to a better perceptual processing in the hemifield contralateral to the DE 104

than in the ipsilateral one. Interestingly, in a subsequent study, the authors found this 105

advantage of the hemifield contralateral to the DE only in participants with strong eye 106

dominance9 according to the peak velocity criterion2. The participants with weak eye 107

dominance exhibited the standard Poffenberger effect (i.e., faster reaction times 108

when both the stimulation and the hand are on the same side8), suggesting that the 109

relationship between DE and ipsilateral V1 and the induced perceptual advantage of 110

the hemifield contralateral to the DE occur only when participants have strong eye 111

dominance. 112

The aim of the present study is to further examine the relationship between DE 113

and ipsilateral V1 and its role in perception and action mechanisms. To do so, we 114

assessed the respective influence of eye dominance (left or right) and of eye 115

dominance strength (strong or weak) on a saccadic task. Participants were instructed 116

to make a saccade toward a lateralized target with a distractor presented 117

simultaneously in the same or in the opposite hemifield. It is now well established that 118

a distractor being presented close to the target position modifies saccade amplitude 119

by deviating the saccade to an intermediate position between the two stimuli (global 120

effect, GE) whereas a distractor remote from the target position increases saccade 121

latency (remote distractor effect, RDE)10-12. We therefore hypothesize that a 122

modulation of both effects, depending on the hemifield in which the distractor is 123

displayed, will reflect the influence of eye dominance and of eye dominance strength 124

on saccadic parameters. Indeed, in participants with strong eye dominance the 125

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perceptual advantage of the hemifield contralateral to the DE should result in a 126

greater impact of the distractor presented in this hemifield compared to the ipsilateral 127

one on saccade amplitude and latency. Conversely, we expect no differences 128

between the two hemifields in participants with weak eye dominance, as found in 129

previous studies based on manual reaction times9. Finally, another manipulation 130

involved varying distractor luminance. It was made either as bright as the target or 131

brighter than the target. Indeed, this manipulation is known to provide greater GE 132

when the distractor is brighter than the target13. Greater perceptual weight given to 133

the distractor should differentially modulate the effects of eye dominance and of eye 134

dominance strength. 135

2. Methods 136

2.1. Subjects 137

Ninety-two right-handed participants were divided into four groups according to 138

their eye dominance (left or right) and eye dominance strength (weak or strong) as 139

defined by the analysis of saccade peak velocity2. This classification was made a 140

posteriori after recording eye movement data (See Figures 1 and 2). Hand 141

preference was determined by using the Edinburgh Handedness Inventory14 and eye 142

dominance by using the hole-in-the-card test1 repeated three times. 143

Insert Figures 1 and 2 Here 144

All of the participants had reported normal or corrected to normal vision. 145

Twenty-two had a strong right DE (4M 18 F; mean age: 22.6 years old, SD: 6.41; 146

mean laterality score: 79%, SD: 22.9%). Thirty-five had a weak right DE (7 M 28F; 147

mean age: 21.3 years old, SD: 2.32; mean laterality score: 81%, SD: 16.2%). Ten 148

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had a strong left DE (1 M 9 F; mean age: 21.9 years old, SD: 3.11; mean laterality 149

score: 77%, SD: 18.8%) and twenty-five had a weak left DE (7M 18 F; mean age: 150

23.8 years old, SD: 6.7; mean laterality score: 83%, SD: 20.9%). 151

They gave their informed consent after an explanation of the procedure. The 152

study adhered to the principles of the Declaration of Helsinki and the procedure was 153

approved by the ethics committee of Paris Descartes University (Comité d’Evaluation 154

Ethique en Recherche Biomédicale, IRB number 20130500001072). 155

2.2. Stimuli 156

The initial central fixation was a 0.5° x 0.5° white cross. The saccade target 157

and the distractor were both a 0.5° x 0.5° white circle. All were displayed on a 158

medium gray background with a luminance of 4.5 cd/m². The fixation cross and the 159

saccade target had a luminance of 27 cd/m² and the distractor luminance was either 160

27 cd/m² or 54 cd/m². 161

2.3. Instruments and Eye Movement Recording 162

Stimuli were presented on an Iiyama HM240DT monitor with a refresh rate of 163

170 Hz and a resolution of 800×600 pixels. The experimental sessions took place in 164

a dimly lit room. Subjects were seated 57 cm away from the screen and their heads 165

kept stable with a chin and forehead rest. Movements of the two eyes were recorded 166

with an Eyelink 1000® (SR Research, Ontario, Canada) sampled at 500 Hz and 167

0.25°. 168

Each session began with a 9-point calibration filling the screen. Before each 169

trial, a small circle was presented at the center of the screen in order to compare the 170

actual eye position with the previous calibration. The participants had to fixate the 171

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circle and press a button on a pad. Trial began when comparison was successfully 172

detected (see procedure). Online saccade detection corresponded to above-173

threshold velocity (30°/s) and acceleration (8000°/s²). 174

2.4. Procedure and design 175

Each participant ran four blocks of 165 trials for a total of 660 trials. The 176

saccade target was always presented in the left hemifield in two blocks and in the 177

right hemifield in the other two blocks. Thus, the uncertainty of target location was 178

reduced by the hemifield blocked design in order to minimize the possible 179

contribution to the distractor effect of decisional and strategy-based processes11. The 180

order of the blocks was counterbalanced across subjects by alternating target side. 181

Each trial of each session began with the presentation of a central fixation 182

cross randomly displayed for 500, 600, 700, 800 or 900 milliseconds. During this 183

delay, the eye position was checked and if the distance between eye position and the 184

center of the cross was greater than 0.75°, the trial was cancelled and repeated later 185

in the session. The initial fixation cross disappeared simultaneously with the target 186

appearance. In the no-distractor control conditions, the target was presented in 187

isolation 3°, 5° or 7° to the left or to the right of the fixation cross on the horizontal 188

axis. In the target-distractor conditions, the target was presented at an eccentricity of 189

5° or 7° to the left or to the right of the fixation cross with a distractor presented at 3° 190

of eccentricity in the same hemifield (testing the GE) or in the opposite one (testing 191

the RDE). Participants were instructed to make a saccade either toward the isolated 192

stimulus in case of no-distractor control condition or to the most eccentric stimulus in 193

case of target-distractor condition. 194

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The whole experiment included 6 no-distractor control conditions (3 195

Eccentricities * 2 Hemifields) and 16 target-distractor conditions testing the GE or the 196

Remote distractor effect (2 target eccentricities * 2 target hemifields * 2 distractor 197

sides * 2 distractor luminances). Each condition included 30 trials. In each block, the 198

target hemifield was held constant whereas all other conditions were intermixed. 199

2. 5. Data Analysis 200

Saccade latency and amplitude were measured. In the no-distractor control 201

conditions, peak velocity of the rightward and leftward saccades was also measured 202

in order to classify participants according to eye dominance strength2. In the target-203

distractor conditions, we also derived two standard additional measures to examine 204

the effect of the distractor on saccadic behavior. The RDE corresponds to the 205

average saccade latency difference between a given experimental condition and its 206

corresponding control condition when the target is displayed at the same eccentricity 207

with no distractor. The global effect percentage15,16 (GEP) was used to examine the 208

deviation of the saccade endpoint induced by the distractor. The GEP was calculated 209

using the following formula: GEP = 100 * ((A3+5or7° - A3°)/( A5or7° - A3°)), where A3° is 210

the average saccade amplitude to targets presented in isolation at 3°, A5or7° is the 211

average saccade amplitude to targets presented in isolation at 5° or 7°, and A3+5or7° is 212

the average amplitude of saccades evoked by target-distractor pairs. A GEP of 0% 213

means that the saccade landed on the distractor position (maximal GE) and a GEP of 214

100% that the saccade landed on the target position (no GE). In other words, the 215

higher the GEP, the lower the GE. All analyses were run using data from both eyes 216

separately. As our hypotheses do not involve any differences between saccadic 217

parameters of the left and right eyes, and as we indeed do not report such 218

differences, we here present only the data from the right eye. 219

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3. Results 220

3.1. Preliminary analyses 221

Trials with blinks (less than 0.01%) and with latency, amplitude or peak velocity 222

outliers diverging from individual distributions (0.06%) were discarded from further 223

analyses. A preliminary analysis showed there was an effect of the block rank on 224

saccade latency (F(3,315) = 8.86, p<.001). Latency was longer on the first block than 225

on the other three blocks. Therefore, in order to keep the number of saccades 226

executed to the left and to the right hemifields constant, the first and the fourth blocks 227

were removed from following analyses. 228

Before analyzing the data on the derived measures to examine the effect of 229

eye dominance and of eye dominance strength on the GEP and the RDE, we 230

conducted a twofold preliminary analysis. We checked that the distractor presented in 231

the hemifield opposite the target increased saccade latency. We also checked that 232

the distractor presented in the same hemifield as the target deviated saccade 233

amplitude. Average saccade latency and amplitude obtained for each condition are 234

presented respectively in Table 1 and 2. 235

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Left Visual Field

T3° T5° T5° D3° T5° D-3° T7° T7° D3° T7° D-3°

Luminance Distractor

D=T D>T D=T D>T

D=T D>T D=T D>T

Right DE Strong 188 (±28) 181 (±22) 184 (±24) 184 (±26) 201 (±30) 199 (±28) 180 (±29) 185 (±31) 184 (±26) 201 (±31) 204 (±29)

Weak 184 (±23) 173 (±18) 179 (±21) 177 (±19) 193 (±20) 193 (±20) 175 (±21) 183 (±20) 182 (±20) 190 (±24) 194 (±27)

Left DE Strong 184 (±25) 177 (±17) 179 (±17) 179 (±19) 195 (±21) 200 (±22) 181 (±18) 182 (±19) 183 (±14) 196 (±26) 198 (±26)

Weak 186 (±19) 180 (±22) 181 (±20) 182 (±19) 193 (±20) 194 (±18) 175 (±15) 184 (±19) 182 (±19) 194 (±18) 191 (±22)

Right Visual Field

T3° T5° T5° D3° T5° D-3° T7° T7° D3° T7° D-3°

Luminance Distractor

D=T D>T D=T D>T

D=T D>T D=T D>T

Right DE Strong 195 (±31) 188 (±22) 188 (±23) 185 (±24) 205 (±28) 203 (±26) 181 (±21) 187 (±23) 188 (±22) 200 (±25) 204 (±28)

Weak 189 (±25) 181 (±24) 183 (±24) 183 (±24) 197 (±27) 198 (±28) 179 (±25) 184 (±22) 187 (±24) 197 (±26) 199 (±29)

Left DE Strong 186 (±16) 177 (±14) 183 (±16) 180 (±16) 196 (±17) 197 (±17) 174 (±17) 182 (±22) 185 (±24) 195 (±18) 197 (±23)

Weak 188 (±22) 180 (±22) 184 (±22) 185 (±20) 199 (±23) 198 (±23) 177 (±20) 186 (±18) 185 (±19) 194 (±19) 201 (±25)

Table 1 : Average latencies (and standard deviations) in milliseconds. Participants were categorized into four groups according to their eye dominance (Right DE; Left DE) 236 and eye dominance strength (Strong; Weak). Their task was to make a saccade toward a target presented either in the Left or in the Right visual field. In no-distractor 237 control conditions, the target (T) could be presented at an eccentricity of 3 (T3°), 5 (T5°) or 7° (T7°) from the initial fixation cross. In target-distractor conditions, the target 238 was presented at an eccentricity of 5 or 7° from the initial fixation cross with a distractor (D) presented either in the same visual field at an eccentricity of 3° (T5° D3° and 239 T7° D3°) or in the opposite visual field at an eccentricity of 3° (T5° D-3° and T7° D-3°). When presented, the distractor could have the same luminance as the target (D=T) or 240 could be brighter than the target (D>T). 241

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243

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244

Left Visual Field

T3° T5° T5° D3° T5° D-3° T7° T7° D3° T7° D-3°

Luminance Distractor

D=T D>T D=T D>T

D=T D>T D=T D>T

Right DE Strong 2.9 (±0.2) 4.7 (±0.3) 4.0 (±0.4) 4.1 (±0.3) 4.8 (±0.2) 4.8 (±0.2) 6.6 (±0.3) 5.8 (±0.5) 5.7 (±0.6) 6.7 (±0.3) 6.7 (±0.3)

Weak 2.9 (±0.2) 4.6 (±0.3) 4.1 (±0.3) 4.0 (±0.3) 4.7 (±0.3) 4.7 (±0.3) 6.4 (±0.4) 5.6 (±0.6) 5.6 (±0.6) 6.6 (±0.4) 6.5 (±0.4)

Left DE Strong 2.8 (±0.2) 4.6 (±0.3) 3.8 (±0.6) 3.9 (±0.5) 4.7 (±0.3) 4.7 (±0.3) 6.5 (±0.4) 5.4 (±1.0) 5.4 (±0.9) 6.6 (±0.3) 6.6 (±0.3)

Weak 3.0 (±0.1) 4.8 (±0.2) 4.1 (±0.3) 4.1 (±0.3) 4.8 (±0.3) 4.8 (±0.3) 6.6 (±0.3) 5.7 (±0.6) 5.6 (±0.7) 6.6 (±0.4) 6.6 (±0.4)

Right Visual Field

T3° T5° T5° D3° T5° D-3° T7° T7° D3° T7° D-3°

Luminance Distractor

D=T D>T D=T D>T

D=T D>T D=T D>T

Right DE Strong 3.0 (±0.2) 4.8 (±0.2) 4.1 (±0.4) 4.1 (±0.4) 4.9 (±0.2) 4.9 (±0.3) 6.6 (±0.4) 5.7 (±0.6) 5.6 (±0.6) 6.8 (±0.3) 6.8 (±0.3)

Weak 3.0 (±0.2) 4.8 (±0.3) 4.2 (±0.3) 4.2 (±0.4) 4.9 (±0.2) 4.9 (±0.3) 6.7 (±0.4) 5.9 (±0.7) 5.8 (±0.8) 6.8 (±0.3) 6.8 (±0.3)

Left DE Strong 3.0 (±0.2) 4.8 (±0.3) 4.2 (±0.4) 4.2 (±0.4) 4.9 (±0.4) 4.9 (±0.3) 6.7 (±0.3) 6.0 (±0.7) 6.1 (±0.6) 6.8 (±0.4) 6.8 (±0.4)

Weak 3.1 (±0.2) 4.9 (±0.2) 4.3 (±0.3) 4.2 (±0.3) 5.0 (±0.2) 5.0 (±0.2) 6.7 (±0.3) 6.0 (±0.6) 5.8 (±0.7) 6.9 (±0.2) 6.9 (±0.3)

Table 2: Average amplitudes (and standard deviations) in degrees. Participants were categorized into four groups according to their eye dominance (Right DE; Left DE) and 245 eye dominance strength (Strong; Weak). Their task was to make a saccade toward a target presented either in the Left or in the Right visual field. In no-distractor control 246 conditions, the target (T) could be presented at an eccentricity of 3 (T3°), 5 (T5°) or 7° (T7°) from the initial fixation cross. In target-distractor conditions, the target was 247 presented at an eccentricity of 5 or 7° from the initial fixation cross with a distractor (D) presented either in the same visual field at an eccentricity of 3° (T5° D3° and T7° 248 D3°) or in the opposite visual field at an eccentricity of 3° (T5° D-3° and T7° D-3°). When presented, the distractor could have the same luminance as the target (D=T) or 249 could be brighter than the target (D>T). 250

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ANOVAs were run on the average saccade latency (Table 1) and on the 251

average saccade amplitude (Table 2) with eye dominance and eye dominance 252

strength as between-subject factors and distractor condition (No distractor, Distractor 253

as bright as the target, Brighter distractor), saccade target eccentricity (5° or 7°) and 254

target presentation hemifield (Left or Right) as within-subject factors. Note that 255

regarding the average saccade latency, the no-distractor control conditions were 256

compared to the opposite-hemifield distractor conditions. Regarding the average 257

saccade amplitude, the no-distractor control conditions were compared to the same-258

hemifield distractor conditions. 259

A main effect of the distractor was found on saccade latency (F(2,176) = 255.52, 260

p<.001) as well as on saccade amplitude (F(2,176) = 505.67, p<.001). As expected, 261

compared to the no-distractor condition, the presentation of a distractor in the 262

opposite hemifield simultaneously with the target induced an increase of 19 ms of 263

saccade latency (F(1,88) = 341.23, p<.001) whereas the presentation of a distractor 264

within the same hemifield induced a deviation of the saccade of 0.8° closer to the 265

distractor (F(1,88) = 341.23, p<.001). RDE and GE were thus well observed in our 266

experiment. 267

3.2. Main results 268

We then conducted several analyses on the derived measures to examine 269

whether the effects of the distractor could be modulated by eye dominance and eye 270

dominance strength. We expected greater effects of the distractor located in the 271

hemifield contralateral to the DE in the case of strong eye dominance and no 272

difference between the two hemifields in the case of weak eye dominance. Average 273

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saccade latency difference (remote distractor effect) and average global effect percentage are presented respectively in Table 3 274

and 4. 275

276

277

278

279

Table 3: Average remote distractor effect (and standard deviations) in milliseconds. Participants were categorized according to their eye dominance (Right 280 DE; Left DE) and eye dominance strength (Strong; Weak). Their task was to make a saccade toward a target (T) that could appear in the left or in the right 281 visual field, at 5 or 7° of eccentricity. Simultaneously with the target, a distractor (D) was presented at 3° of eccentricity in the visual field opposite the target. 282 This distractor could either have the same luminance as the target (D=T) or be brighter than the target (D>T). 283

284

285

286

287

288

289

290

291

Left Visual Field Right Visual Field

T5° D3° T7° D3° T5° D3° T7° D3°

Luminance Distractor D=T D>T D=T D>T D=T D>T D=T D>T

Right DE Strong 19 (±17) 18 (±13) 21 (±13) 24 (±12) 17 (±21) 15 (±14) 20 (±14) 24 (±15)

Weak 20 (±11) 19 (±11) 15 (±12) 19 (±15) 16 (±15) 17 (±12) 18 (±17) 19 (±16)

Left DE Strong 18 (±9) 23 (±11) 15 (±17) 17 (±18) 19 (±14) 21 (±16) 21 (±10) 23 (±13)

Weak 13 (±10) 14 (±14) 20 (±14) 16 (±17) 19 (±18) 18 (±12) 17 (±13) 24 (±20)

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292

293

294

295

296

297

298

Table 4: Average global effect percentage (and standard deviations). Participants were categorized according to their eye dominance (Right DE; Left DE) and 299 eye dominance strength (Strong; Weak). Their task was to make a saccade toward a target (T) that could appear in the left or in the right visual field, at 5 or 7° 300 of eccentricity. Simultaneously with the target, a distractor (D) was presented at 3° of eccentricity in the same visual field as the target. This distractor could 301 either have the same luminance as the target (D=T) or be brighter than the target (D>T). Remember that the higher the GEP, the lower the distractor effect on 302 saccade amplitude. 303

Left Visual Field Right Visual Field

T5° D3° T7° D3° T5° D3° T7° D3°

Luminance Distractor D=T D>T D=T D>T D=T D>T D=T D>T

Right DE Strong

63.0 (±12.4)

63.6 (±13.9)

78.0 (±9.9)

76.2 (±11.9)

62.4 (±14.1)

59.9 (±14.1)

74.0 (±13.4)

71.3 (±12.2)

Weak 67.2

(±10.2) 63.4

(±9.2) 75.7

(±13.2) 76.0

(±11.9) 69.7

(±11.3) 69.5

(±13.2) 78.4

(±15.9) 76.1

(±17.5)

Left DE Strong

55.8 (±19.5)

57.1 (±16.1)

68.7 (±21.8)

68.2 (±17.4)

69.4 (±12.2)

65.9 (±11.8)

81.4 (±12.0)

84.8 (±10.4)

Weak 64.5

(±12.3) 62.8

(±11.6) 74.7

(±12.9) 73.6

(±15.8) 68.8

(±11.7) 64.6

(±13.2) 78.5

(±14.4) 74.7

(±15.7)

16

Two ANOVAs were conducted on the average saccade latency difference 304

(Table 3) and on the GEP (Table 4) with eye dominance (Left or Right) and eye 305

dominance strength (Strong or Weak) as between-subject factors and saccade target 306

eccentricity (5° or 7°), hemifield of target presentation (Left or Right) and distractor 307

luminance (Same or Brighter than the target) as within-subject factors. Concerning 308

the average saccade latency difference (Table 3), we found no main effect or 309

interaction between factors (all p>.10) with the exception of a significant effect of the 310

distractor luminance (F(1,88) = 4.57, p<.001). Saccade latency increased very slightly 311

with a brighter distractor (1.5 ms on average). Data on the GEP (Table 4) indicated a 312

significant effect of target eccentricity (F(1,88) = 131.95, p<.001): GE was higher with 313

shorter target-distractor distance (difference of 11.5%). Distractor luminance also 314

significantly affected GE (F(1,88) = 9.82, p<.005): GE was higher with a brighter 315

distractor with a very slight difference (1.4%). We found no main effect either of eye 316

dominance (F<1) or of eye dominance strength (F(1,88) = 1.05, ns). However, a main 317

effect of the hemifield of presentation was found (F(1,88) = 7.73, p<.01), the deviation 318

of the saccade toward the distractor being greater in the left hemifield (69.1%) than in 319

the right one (71.6%). More interestingly for our purpose, such an effect interacted 320

with eye dominance and eye dominance strength (F(1,88) = 8.86, p<.005). Figure 3 321

presents this interaction between eye dominance (left or right) and hemifield (left or 322

right) in participants with strong (figure 3a) and weak (figure 3b) eye dominance. The 323

effect of the hemifield of presentation did not reach the significance threshold for 324

people with weak eye dominance (F(1,58) = 2.975, p<.10) regardless of their DE (F<1), 325

whereas it was amplified in participants with a strong left DE, the saccade being more 326

deviated toward the distractor presented in the left than in the right hemifield (62.4% 327

vs 75.4%, F(1,9) = 11.92, p<.007). Participants with a strong right DE seemed to show 328

17

the reverse effect, with a distractor impact greater in the right hemifield than in the left 329

one, but the difference failed to reach the significance threshold (Figure 3a, F(1,21) = 330

2.92, p<.10). However, it should be noted that an effect of eye dominance strength 331

was found in the right hemifield in participants with a right DE (F(1,55) = 3.87, p<.05) 332

with the distractor effect being greater in participants with strong eye dominance 333

(66.9%) than with weak eye dominance (73.4%). 334

Insert Figure 3 Here 335

4. Discussion 336

4.1. Measuring eye dominance strength: The peak velocity criterion 337

Analyses of saccade peak velocities have been shown useful to estimate eye 338

dominance strength based on binocular recording of eye movements made toward 339

an isolated target2. Accordingly, participants exhibit higher peak velocities toward the 340

hemifield ipsilateral to the DE in case of strong eye dominance and exhibit a naso-341

temporal asymmetry3 in case of weak eye dominance2. However, note that 2 of the 342

18 participants in the 2012 study exhibited higher peak velocities toward the 343

hemifield contralateral to DE whichever eye they used. In the present study, when we 344

categorized the 92 participants according to eye dominance strength, we noticed that 345

those with strong eye dominance also did not systematically exhibit higher peak 346

velocities toward the hemifield ipsilateral to the DE (see Figure 1). Indeed, 37.5% 347

(12/32) exhibited higher peak velocities toward the hemifield contralateral to the DE. 348

However, the results on the GEP for those 12 participants matched the patterns 349

observed in their eye dominance groups as defined by the hole-in-the-card test, with 350

lower GE (i.e., higher GEP) in the hemifield contralateral to the DE than in the 351

18

ipsilateral one. Therefore, these results on GEP as well as the different patterns of 352

peak velocities in the two studies suggest that the criterion for strong eye dominance 353

should finally be to exhibit higher peak velocities toward the same hemifield (left or 354

right) with both eyes, and not only toward the hemifield ipsilateral to the DE. 355

4.2. Distractor Luminance 356

In order to manipulate the perceptual weight of the distractor, the distractor 357

was either as bright as the target or brighter. We did not find a strong modulation of 358

the distractor effect neither for the remote distractor effect nor for the global effect. In 359

remote distractor effect conditions, we observed an only very slight effect of distractor 360

luminance on saccade latency, but no interaction with eye dominance, eye 361

dominance strength or hemifield. A very slight effect of distractor luminance was also 362

found on the GEP. Overall, the manipulation of distractor luminance we used 363

appeared to be not enough important to modify the pattern of results depending on 364

eye dominance and eye dominance strength. 365

4.3. Remote distractor effect 366

A distractor displayed in the hemifield opposite the target hemifield produced a 367

RDE. However, neither eye dominance nor eye dominance strength modulated this 368

effect. Unlike saccade amplitude or saccadic peak velocity2, the presence of 369

asymmetries on saccade latency is unclear in the literature: some studies reported 370

average left-right asymmetries17,18 while others not19,20. However, these studies never 371

took into account eye dominance or even manual laterality. Very few studies have 372

looked the effect of eye dominance but again without consistent results2,21,22. The 373

present study tested these asymmetries on a large sample of participants, and failed 374

to find any left-right asymmetries on saccade latency. The fact that RDE did not differ 375

19

between the two hemifields in participants with strong eye dominance suggests that 376

eye dominance does not influence saccade latency, at least in the conditions we 377

tested. 378

4.4. Global effect 379

When the distractor was in the same hemifield as the target, our results show 380

that the distractor had more impact on saccade amplitude (GE) when presented in 381

the hemifield ipsilateral to the DE than in the contralateral one. This was true only in 382

participants with strong eye dominance. However, this contrasts with our assumption 383

based on findings involving the presentation of a unique stimulus2,7,9. Interestingly, 384

the presentation of two stimuli, one of which is the saccade target as used in the 385

present study, specifies the perceptual processing advantage of the hemifield 386

contralateral to the DE, which would finally not occur in the overall hemifield, but 387

would be restricted to the saccade target location. Therefore, in a saccadic task we 388

suggest that the relationship between DE and ipsilateral V1 would lead to a more 389

accurate selection of the saccadic target in this hemifield (i.e., smaller effect of the 390

distractor on saccade amplitude) than in the ipsilateral one. 391

Note that the accurate selection of the saccadic target in the hemifield 392

controlateral to DE for participants with strong eye dominance is hypothesized in light 393

of the relationship between DE and ipsilateral V1, but V1 is only the starting point of 394

the sensori-motor transformation. The signals are then transmitted to the parietal eye 395

fields in the posterior parietal cortex and to the frontal eye fields, close to the 396

precentral sulcus23,24. So, it remains open whether the relationship between DE and 397

ipsilateral V1 will then lead to left-right asymmetries in parietal eye fields and frontal 398

eye fields activations. Future neuroimaging studies could help to clarify this point, 399

20

contrasting participants with left and right dominant eye, strong and weak eye 400

dominance. 401

However, our results showed a clear difference between the two hemifields in 402

participants with a strong left DE, but the difference was slighter and did not reach 403

the significance threshold in participants with a strong right DE. To explain this 404

difference between those two groups we propose that two phenomena are involved: 405

on the one hand, in participants with strong eye dominance, the relationship between 406

DE and ipsilateral V1 would induce a more accurate selection of the saccadic target 407

in the hemifield contralateral to the DE than in the ipsilateral one. On the other hand, 408

there would be an attentional bias toward the left hemifield giving more weight to the 409

distractor due to the specialization of the right hemisphere for visuo-spatial 410

attention25-28. Note that this attentional bias is hypothesized for all the participants, 411

and may explain that the distractor deviated saccade amplitude more when 412

presented in the left than in the right hemifield in participants with weak eye 413

dominance (see Figure 3b). 414

Insert Figure 4 Here 415

Figure 4 separately summarizes those two phenomena in participants with a 416

strong left and right DE. In participants with a strong left DE, each phenomenon 417

occurs separately in one hemifield and does not counteract the other one, leading to 418

a great GEP difference between the two hemifields. Conversely, those two 419

phenomena occur in the same hemifield in participants with a strong right DE. 420

Moreover, the attentional bias that gives more weight to the distractor counteracts the 421

accurate selection of the saccadic target. Accordingly, a smaller GEP difference 422

between the two hemifields was found in this population. 423

21

5. Conclusion 424

Researchers can now precisely measure participants’ handedness based on 425

questionnaires assessing a percentage of handedness. However, eye dominance is 426

still evaluated based on binary measures. Much research has been carried out to 427

develop a more graduated measure of eye dominance2,9,29-35. We here show different 428

visuomotor influences of eye dominance according to eye dominance strength. 429

Moreover, the use of two stimuli helped to specify the link between DE and ipsilateral 430

V1 (previous studies used a simple target stimulus2,7,9). Indeed, the better processing 431

that it involves in the hemifield contralateral to the DE seems not to operate in the 432

whole hemifield, but seems restricted to the saccade target location. These findings 433

point out the importance of taking into account participants’ eye dominance and eye 434

dominance strength in further visual or visuomotor studies. 435

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Figure legends: 519

Figure 1: Average differences of peak velocities of saccades toward isolated targets 520

in left and right visual fields indicating strong eye dominance. 521

Participants were categorized into two groups according to their eye 522

dominance (Left or Right) measured with the hole-in-the-card test. Negative values 523

indicate that saccades toward the left visual field exhibit higher peak velocities than 524

saccades toward the right visual field, and positive values indicate the opposite. 525

Those differences have been calculated for saccades made toward isolated targets 526

presented at 3, 5 or 7° of eccentricity for the right eye (R eye) and the left eye (L 527

eye). All the participants presented in this graph exhibit higher peak velocities toward 528

a same visual field whatever the eye being measured for at least two of the three 529

eccentricities tested. Therefore, they have been categorized as having strong eye 530

dominance. 531

Figure 2: Average differences of peak velocities of saccades toward isolated targets 532

in left and right visual fields indicating weak eye dominance. 533

Participants were categorized into two groups according to their eye 534

dominance (Left or Right) measured with the hole-in-the-card test. Negative values 535

indicate that saccades toward the left visual field exhibit higher peak velocities than 536

saccades toward the right visual field, and positive values indicate the opposite. 537

Those differences have been calculated for saccades made toward isolated targets 538

presented at 3, 5 or 7° of eccentricity for the right eye (R eye) and the left eye (L 539

eye). All the participants presented in this graph exhibit higher peak velocities toward 540

the right visual field with the right eye and toward the left visual field with the left eye 541

(i.e., naso-temporal asymmetry) for at least two of the three eccentricities tested. 542

Therefore, they have been categorized as having weak eye dominance. 543

26

Figure 3: Interaction between Eye dominance strength, Eye dominance and 544

Visual field on Global Effect Percentage (GEP). 545

Figure 3a shows the interaction between Eye dominance (L = left DE; R = right 546

DE) and Visual field (LVF = left visual field; RVF = right visual field) in participants 547

with strong eye dominance. Figure 3b shows the same interaction in participants 548

with weak eye dominance. In both graphs, the significant differences are indicated 549

with the symbol * (p<.05) and the differences that failed to reach significance with 550

the symbol ≈ (.05<p<.10). Error bars represent standard errors. 551

Figure 4: Illustration of the two phenomena inferred from our results on the global 552

effect percentage (GEP). 553

Black indicates the relationship between DE and ipsilateral V1, leading to a 554

more accurate saccadic selection in the visual field contralateral to the DE than in 555

the ipsilateral one. This phenomenon occurs in opposite visual fields in 556

participants with a strong left DE (Figure 4a) and with a strong right DE (Figure 557

4b). Gray indicates the second phenomenon, an attentional bias toward the left 558

visual field due to the right hemisphere specialization for visuo-spatial attention, 559

giving more weight to the distractor in this visual field than in the right one. 560

561

27

Figure 1: 562

563

564

Figure 2: 565

566

567

568

28

Figure 3: 569

570

571

Figure 4: 572

573